We took a pampas tour down this river with a reputable company in Rurrenabaque. We were unlucky to arrive in Santa Rosa port on a rainy day so as soon as we got on the small canoe, we did see some birds, but it was rather dissapointing as there were no alligators nor capybaras. The next day, our guide took us up river and we never saw so many animals. Apparently, the sun makes the animals flock to the riverbed and it was amazing to see squirrel monkeys, caymans, sereres, even a sloth and tons of birds. Of course it is something you cannot control, but avoid going in the rainy season, as you will see some animals but not like this place has the potential to show.